BQ⁺ reduces the P_o of Cx50 hemichannels in excised patches. Shown on top is a recording of a single Cx50 hemichannel in an outside-out configuration at a membrane potential of −50 mV. The application of 500 µM BQ⁺ to the extracellular face of the hemichannel caused a robust reduction in the P_o of the hemichannel, evident by transitions of the hemichannel to the fully closed state (dotted line). The reduction in P_o was reversible upon washout of BQ⁺. Amplitude histograms shown in the bottom panels indicate that the amplitude of the fully open state was not affected in the presence of 500 µM BQ⁺. Histograms were obtained from the current recording during the application of BQ⁺ (left) and after washout of BQ⁺ (right).